The present invention is related to the following GE applications Ser. No. 11/809,122, filed on May 31, 2007, respectively.
The invention relates generally to a topology for a three-phase, wye-connected H-bridge converter that allows continued operation when one H-bridge phase has failed and more particularly to a topology that reduces power losses in semiconductor switches, allowing the wye-connected H-Bridge converter to put out more current with the same temperature rise in the power switches.
High-speed, high-power electric motors (HSEM) that operate at variable speed are increasingly required in a range of industrial, mining and drilling activities. Further, the activities often require a high-degree of reliability. In operations such as crude oil pumping from remote global locations where access to pumping stations is difficult and time-consuming, reliability of motor operation is necessary to prevent dangerous, costly and extended outages. Simple, sturdy and reliable power converters are requisites for such high-speed, high-power motor operations. It is well known that providing multiple individual components, such as series or parallel semiconductor switches, may increase the likelihood that any one individual component switch may randomly fail. Added elements such as snubber circuits for semiconductor switches, further increases the number of components that can fail. It is desirable to arrange the power converter in a simple configuration, with as low a part component count as is possible. However, individual components such as the semiconductor switches for the power converted must be operated with satisfactory margin to thermal and other functional limits to prevent failures in the simplified configuration.
A simplified three-phase, wye-connected H-bridge converter 10 configuration is illustrated in FIG. 1. Each phase of the converter includes a power source/sink 20 with a dc power shaping circuit, represented by capacitor 30. The power source/sink/20 and dc power shaping circuit, represented by capacitor 30, establish a dc-bus voltage input to the semiconductor switches of the bridge. Insulated-gate bipolar transistors (IGBTs) 40 with built-in diodes 45 may form each leg of the H-bridges 50, for example, but other power semiconductor switches such as integrated-gate commutated thyristors (IGCTs) or metal-oxide semiconductor field-effect transistors (MOSFETs) could be used instead. The type of power semiconductor switch is not important to the analysis. Each H-bridge includes two legs, an output leg 60 and a neutral leg 65. Each phase output, phase A 70, phase B 75 and phase C 80, is connected to the midpoint 85 of the respective output bridge leg 60. Each neutral connection to wye-point 90 is tied to the midpoint 95 of the respective neutral output leg 65.
Gating controls 115 may provide control signals 116, 117, 118 for switching semiconductor switches 40 of Phases A, B and C of the H-bridge converter 10, according to predetermined switching patterns. Gating controls may provide for synchronous switching or asynchronous switching to the semiconductor switches 40 of the H-bridges 50.
While the above-described three-phase, wye-connected H-bridge converter provides simplicity, should failure occur in one of the phase H-bridges, operation of large high-speed electric motors (HSEMs) loads will be interrupted.
Accordingly, to assure availability of operation of the motor loads, it is desirable to provide a converter topology that can survive failure of any one phase of the H-bridge circuit, but at the same time reduce switching losses and harmonic distortion.